1. Field of the Invention
The present invention relates to a brake system for a vehicle and, more particularly, to an inboard brake system for a straddle-type all-terrain vehicle.
2. Description of Related Art
All-terrain vehicles (ATV's) generally utilize front and rear brake systems. Prior front brake systems have included disk or drum brake assemblies that are mounted to each front wheel assembly. For example, it is known in the art to mount a brake disk to the hub of each front wheel assembly that is engagable by a brake caliper. Each brake caliper is rigidly mounted to the upright structure of each wheel assembly, and is driven by a hydraulic or cable system that is actuated using a hydraulic or mechanical lever mounted on the handlebars. Additionally, it is known to mount a brake drum to the hub and provide a pair of brake shoes engagable with the brake drum to effect braking. The brake shoes and an actuating mechanism (typically includes a piston and adjuster) are mounted to the upright structure of the wheel assembly within an inner periphery of the brake drum and are non-rotatable relative to the brake drum. Similarly as with disk brakes, drum brakes may be driven by a hydraulic or cable system actuated using a hydraulic or mechanical lever mounted on the handlebars.
These types of front braking systems provide adequate braking force, but have several disadvantages. For example, mounting the brake assemblies to the front wheel assemblies exposes the components of the brake assemblies, such as the brake disks or drums, calipers, and brake lines, to damage from obstacles such as rocks and other debris. Furthermore, the weight that is carried by the suspension is increased since the entirety of each brake assembly is mounted on the respective wheel assembly. As such, there is more weight on moving parts of the suspension system requiring these parts to be stronger. Strengthening the suspension system generally requires heavier and/or more expensive parts. Furthermore, it may be more difficult to precisely tune or calibrate the suspension system, especially shocks and/or springs, to provide a comfortable ride.
Prior rear brake systems include those that have been used on ATVs that have chain driven rear axles. These brake systems generally have a single brake disk mounted on the rear axle. These types of brake systems however usually lead to chain stretching, which may cause damaging backlash due to slack in the chain. Upon braking, take-up of slack in the chain causes jarring of the ATV. The jarring can cause fatigue wear of the rear axle components.
An alternative to this type of rear brake system includes rear disk brake assemblies that are mounted to at least one of the rear wheel assemblies. These systems are applicable to ATVs that have chain-driven or shaft-driven rear axles. However, as with the similar front disk brake systems, these rear disk brake systems are prone to damage from debris and increase the sprung weight of the rear suspension. Furthermore, four wheel drive-type all-terrain vehicles that have these types of brake systems are also subject to damaging backlash within the rear drive assembly, which typically includes a gear box. Backlash is caused when braking power is transferred from, e.g., the rear brakes to the front of the vehicle through the rear drive assembly and drive line. The braking power that is transferred through the rear drive assembly is subject to play between gears within the gear box. When the brakes are engaged, the output of the rear drive assembly effectively slows or stops and the rear drive assembly is jarred as the engine takes up the play within the gearing of the gear box. The jarring can cause excessive wear and fatiguing of the gears and result in damage to the rear drive assembly.
Another type of rear brake system for an all-terrain vehicle is described in U.S. Pat. No. 5,775,457 that includes a drum brake assembly that is integral with the rear gear box. The drum brake assembly is mounted adjacent the gearing of the gear box and internally of the gear box housing. This type of brake system may decrease backlash somewhat, however is costly to manufacture.
Further, a rear disk brake system has been used that utilizes a single disk brake assembly that is mounted to the engine/transmission end of the drive shaft connecting the rear drive assembly to the transmission. In this system, the brake disk is mounted to a hub disk that is rotatable with the drive shaft. The caliper is mounted to either the engine or the transmission to be engagable with the brake disk. This system is disadvantageous in that the brake system is exposed to the high heat conditions of the engine and transmission. Prolonged exposure to high heat conditions is detrimental to brake pad and brake disk life and reduces braking effectiveness and efficiency.